The present invention relates to an apparatus for redirecting air flow, and more particularly, to an apparatus for efficiently redirecting a horizontal, planar, radially inward directed air flow ninety degrees to a vertically directed air flow having a generally uniform velocity profile. Additionally, the present invention provides an apparatus for directing a three-dimensional inward directed air flow to a planar radially inward directed flow as well as an apparatus for directing an air flow having a generally uniform velocity profile to the inlet of a ducted fan.
Wind tunnels can generally be open circuit designs, wherein the air is drawn from and discharged to the ambient atmosphere, or closed circuit designs, wherein the air is recycled. In the case of an open circuit design, in order to create a vertically discharged air stream, prior art wind tunnels have used a vertically oriented fan to directly accelerate air which is exhausted to an upper exit section. Wind tunnels such as these have been used for recreation, such as re-creating a free-fall environment for training sky divers, or for scientific and research purposes. When such a tunnel is used for recreational or training purposes, a user is placed directly into the accelerated air flow, which acts upon the user""s body with sufficient force so as to suspend the user""s body at a certain elevation. The user is thus maintained in the elevated position until the user is removed from the flow of air, or the air flow is reduced or terminated. When used for research purposes, an object to be studied is placed in the air stream so that measurements can be taken. Commonly, smoke tracers are also used so that the air flow around the object can be observed. In either usage, a relatively uniform velocity profile is highly desirable.
However, existing vertical wind tunnels as described above have several drawbacks for these usages. For example, in recreational circumstances, the user is either elevated directly over or directly beneath the fan or blower motor and is therefore subjected to noise levels loud enough that ear plugs may be required to reduce the sound to a tolerable level. Furthermore, the air flow emanating from the fan is generally quite turbulent and has an uneven velocity profile, which leads to rough conditions for the user and unpredictable variables for the researcher. These problems are increased by the fact that most vertical wind tunnels of this type utilize a standard aircraft propeller to accelerate the air which further contributes to the heightened noise levels and the uneven velocity profiles.
Additionally, the positioning of the fan motor in a vertically upright orientation presents its own set of engineering obstacles. First, in order to create the desired laminar flow, the length of the entire assembly from the fan drive motor to the upper exit section can be quite long. Therefore, in order to house the necessary equipment and place the upper exit section of the wind tunnel at an easily accessible location, either significant excavation or construction of an elevation structure must be completed which can greatly increase the expense and complexity of the wind tunnel construction. Furthermore, additional ductwork has to be built to provide inlet air for the fan, further adding to construction expense. Even more significantly, though, is the fact that the vertical orientation of the fan motor places more stress on the motor bearings than a horizontal orientation would, thereby increasing maintenance expense and reducing the life span of the motor.
In order to overcome these problems, wind tunnels have been built to create vertical air flows using generally horizontally oriented fans. For example, prior art wind tunnels have been made for creating a vertical air flow using horizontal fans whereby the horizontal fan accelerates air through a run of horizontal ductwork after which the air is turned to a vertical direction using a vertically angled baffle. However, prior art apparatuses using this method have encountered problems. For instance, the velocity profile of the air flow leaving the tunnel is not as uniform or consistent as is generally required or desired. Furthermore, the baffles used for redirecting the flow is very inefficient, resulting in unacceptable energy losses, and therefore lower than desired air flow velocities.
Accordingly, there is a need for an apparatus for creating a vertical flow of air which provides relatively uniform flow velocities, which is relatively quiet in operation, which is of simple design and construction, and which can be assembled and maintained at a low cost. Accordingly, there also exists a need for an apparatus which can efficiently redirect air flow from a generally horizontal direction to a generally vertical direction. There also exists a need for an apparatus which can redirect a three-dimensional, inward directed air flow to a generally planar radially-inward directed flow. Furthermore, there exists a need for an apparatus that can redirect air flow in the above-noted manners in an efficient manner while maintaining relatively high energy ratios.
It is an object of the present invention to provide an apparatus for redirecting air flow from a generally horizontal flow to a generally vertical flow in an efficient manner. The present invention also efficiently redirects a three-dimensional, inward directed air flow to a generally planar radially-inward directed flow.
The apparatus of the present invention redirects air flow from a generally horizontally-directed flow to a generally vertically-directed flow by first creating a three-dimensional horizontally directed air flow from a horizontally mounted ducted fan. This three-dimensional flow is then directed into the bottom of a vertically oriented nozzle in a radially inward manner. Finally, the radially inward directed flow is converted to a vertically outward directed flow, and is forced out through the nozzle. The redirection of the flow from a radial inward to a vertically outward direction is accomplished by means of a stagnation zone formed in the nozzle by the impingement of all of the inward flows upon each other. The redirection from a three-dimensional inward flow to a generally planar, radially inward flow is accomplished by a scroll.
While the scroll can be of any shape which is capable of converting the three-dimensional flow to a generally planar, radially inward flow, preferably it is in the shape of two symmetric chambers or a spiral, or more preferably, a hyperbolic spiral. If the symmetric chambers are used, the horizontally directed three-dimensional flow is split before reaching the nozzle and directed so that each chamber receives roughly one-half of the flow. Each chamber then operates to efficiently distribute the air radially inward on a plane to the center point of the nozzle, which is distributed evenly above both chambers.
Alternatively, if a hyperbolic spiral is used, the horizontally directed three-dimensional flow is diverted around the circumference of the nozzle such that the air is proportionally distributed on a plane into the nozzle until the flow is substantially dissipated, any remaining air being directed to rejoin the incoming flow. In either case, the flow enters the bottom of the nozzle on a generally horizontal plane and is directed radially inward as it enters the nozzle by a series of shaped guide vanes.
Upon approaching the center point of the nozzle, a stagnation zone is formed as the individual radially inward directed flows impinge upon each other. This stagnation zone has a high degree of static pressure and takes the form of an upwardly protruding cone which operates to smoothly and efficiently direct the air upwards through the opening in the nozzle. Thus the flow exiting the nozzle is efficiently redirected in a vertical direction and has a generally uniform velocity profile.
The use of nozzles for directing fluid flow is well known in the art. In particular, it is known to use a converging nozzle in an internal combustion engine to direct air into the carburetor. However, in most prior art applications using nozzles, the inlet to the nozzle is connected to a relatively large plenum. In these applications it is considered highly desirable to keep obstructions away from the nozzle inlet so that the fluid flows into the nozzle in an undisturbed, laminar flow. Accordingly, designers of these prior art systems would not think to position a nozzle as it is positioned in the present invention, namely with the inlet in close proximity to a flat, solid surface. In fact, this convention would be the antithesis of what would generally be considered a desirable design feature. Additionally, it is noted that while guide vanes are taught in prior art closed-circuit wind tunnel designs for directing air flows around the corners of the closed-circuit tunnels, it is believed that the use of guide vanes as disclosed in the present invention to create radially inward flows which impinge upon each other to create a stagnation zone is heretofore unknown.
The present invention further provides a wind tunnel having a horizontal lead-in with an exit which is normal to the lead-in. This arrangement allows the motor and fan to be remotely placed from the user, and provides a much quieter environment than is provided in prior art vertical configurations. Furthermore, the horizontal section also allows for greater control over the air flow. Thus a generally even, uniform flow may be generated. Also, the horizontal lead-in section of the present invention avoids the problems associated with the extensive excavation required for the entirely vertically oriented tunnels of the prior art.
Additionally, the present invention allows the use of a ducted fan in place of fans with standard propellers, as used in the prior art. Ducted fans are desirable because the geometry around the ducted fan, including the fan inlet ducts, may be more easily controlled as well as the fact that ducted fans are quieter and more efficient than standard propellers. Therefore, by using an inlet bell having an appropriate shape, the flow into the fan can be manipulated to produce a flow coming out of the fan having the desired, more uniform, velocity profile. Accordingly, it is an additional objective of this invention to provide an inlet bell having a structure similar to the outlet nozzle of the present invention which utilizes a stagnation zone to redirect air efficiently into the inlet of a ducted fan.
Accordingly, the present invention provides for an apparatus for redirecting airflow from a generally three-dimensional, inward directed flow to a generally planar, radially inward directed flow, and then to a vertically outward flow having a uniform velocity profile. The apparatus comprises a generally planar support surface and a converging nozzle arranged such that the nozzle axis is generally perpendicular to the support surface. The nozzle is spaced apart from the support surface to create a nozzle opening to receive the radially-inward directed air flow. The nozzle has a curvature, preferably ellipsoid in shape, selected such that a three-dimensional pressure distribution or stagnation zone is created in the lower portion of the nozzle when air flows radially inwards through the nozzle opening, thereby aiding in the redirection of the air vertically outward.
These and other objects and advantages of the present invention will be more fully understood and appreciated by reference to the following description, the accompanying drawings and the appended claims.